Applicant claims priority under 35 U.S.C. xc2xa7119 of Austrian Application No. A 76/99 filed Jan. 21, 1999. Applicant also claims priority under 35 U.S.C. xc2xa7120 of PCT/AT00/00015 filed Jan. 21, 2000. The international application under PCT article 21(2) was not published in English.
The present invention relates to a chain stitch sewing machine having a needle bar mounted in a housing in such a way that it can be lifted and driven and at least one sewing needle which can be fixed on the needle head of the needle bar, to which a sewing thread can be fed by a thread spool by means of a tightener and a thread guiding device, whereby the thread guiding device comprises a thread takeup controlling the tension of the thread depending on the lift of the needle bar.
These sewing machines sew according to the chain stitch principle, whereby the sewing thread loops formed respectively during a needle insertion is guided through by the thread loop of the same or another sewing thread of the preceding stitch and is held by the following thread loop. The chain stitch can be formed with one or more sewing threads and the chain stitches are suited to tensed stitches and the sewing of elastic textiles due to their ductility. In the process the thread takeup plays an important role, since it must provide the quantity of sewing thread required for the stitching procedure, take them back again after the looping of surplus threads and tighten the thread looping thus formed. Known thread takeups have a thread eyelet integral with the housing and a thread eyelet which can be moved up and down with the lift of the needle bar, giving rise to a thread tension dependent on the lift of the needle on account of the relative movement of both eyelets.
Stoppage of the thread takeup and a thread-guiding procedure insufficient for the critical stitch formation phases occur however during the lifts of the needle bar as the lower and upper dead centers are reached, by means of which for example the thread looping is tightened only partially by means of the thread takeup, but also partially by the advance of the material to be sewn and the material is drawn together because of the thread tension to be increased, resulting in unwanted crimped and gathered sewn areas in the case of elastic textiles.
The object of the present invention is therefore to provide a chain stitch sewing machine of the type initially described, which allows the sewing of flawless, even chain stitches by means of an improved thread guiding device also with highly elastic sewing materials.
The invention solves this task by the fact that the thread takeup has a feed disk resting on a feed shaft which can be driven synchronously to the needle bar, which forms on the periphery side an eccentric takeup cam for takeup of threads and with this takeup cam projects between two thread eyelets supported fast to the housing for the sewing thread running transversely to the feed disk by way of the takeup cam, and/or a thread control device is mounted in the direction of thread tightening downstream of the thread takeup for each sewing thread, which thread control device respectively has a control disk resting on a control shaft which can be driven synchronously to the needle bar with a control cam on the periphery side for the sewing threads guided by two thread eyelets supported fast to the housing on both sides of the control disk by way of the control disk.
By use of a rotating feed disk as thread takeup the sewing thread can be controlled according to the run of the takeup cam rotating with the feed disk relative to the stationary thread eyelets and be provided and taken back in a thread quantity adapted to the respective stitching procedure, without having to observe stoppage determined by the dead center, such that in particular thread tension and tightening of the thread looping are enabled essentially by the thread takeup alone. The reactions of the thread tensions on the sewing material are accordingly minimal and crimping of seams and the like are extensively avoided. The feed shaft drive can be easily diverted by the rotary drive of the needle bar and the feed disk can be designed as single or double disk and also be fitted with a thread stripper or the like for guiding threads in the vicinity of the takeup cam.
If a thread control device according to the present invention is provided in addition to the thread takeup, the tension of each sewing thread can be stabilised individually and controlled and adapted to the stitching procedure belonging thereto especially. This thread control device can be combined with a conventional thread takeup, though there is understandably a better control and coordination option for the thread tension with a combination with the new thread takeup, which can then have a feed disk common to all sewing threads. The thread takeup and its influence on the thread tension are thus overridden by the thread run conditions on the basis of the control disks, by means of which the thread tension required for each sewing thread can be adjusted exactly to the thread tension required for the respective stitching procedure. The advance or retraction of the thread resulting during the to-and-fro stitching motion of the sewing needle depending on the path of the takeup cam on the one hand and the respective control cam on the other hand produces precise stitching, without noticeable reaction to the sewn material, whereby the widest range of chain stitches can be created perfectly and with optimum quality with one or more sewing needles and one or more sewing threads assigned thereto.
The control shaft is effectively designed as an extension of the feed shaft, so that a common drive results for the thread takeup and the thread control device, If several sewing threads and thus also several thread control devices are provided, the control disks of all thread control devices can sit on one and the same control and feed shaft.